Every year, the North American Butterfly Association (NABA) sponsors a “July 4th” butterfly count; it’s a count of all the species volunteers spot within a 15-mile radius on a particular day in the 4 weeks before or after July 4th. In San Francisco, it’s usually organized by Liam O’Brien who keeps the www.sfbutterfly.com website and blog.

This year, it very nearly didn’t happen. Blame it on the fog.

The count was scheduled for June 14th. The weather was cold and drizzly – San Francisco’s storied summer weather – and it was cancelled. That left little time for a reorganized Count. But with luck and determination, it did happen on July 24th – though with only 16 people participating instead of the 34 who took part last year. They spotted some 919 individual insects (compared with 967 or 990, not sure which, in 2011).

In 2010, it was held on June 7th on a foggy day; in 2012, it was held on July 3rd, a month later and the weather was bright and sunny. This time, it was foggy but clearing to sunshine on July 24th, 2012. As the timing and weather changes, so do the butterflies seen. This year, they again saw 26 species of butterfly (26 last year, 24 in 2010), including the Western Pygmy Blue and the Propertius Duskywing for the first time. Some species seen in 2010 or 2011 didn’t show this year.

As in the two prior years, the Cabbage White butterfly easily topped the list. This year, they accounted for nearly a quarter of the butterflies spotted, which is down from over 40% in 2010. But the second most common keeps changing:

California Common Ringlet by David Hoffman (Creative Commons)

In 2010, it was the tiny brown Umber Skipper, (which didn’t even make the top ten this year). In 2011, it was the handsome Anise Swallowtail. And this year, the Sandhill Skipper and the California Common Ringlet – both small brown butterflies – tied for second place.

The Anise Swallowtail, which depends on fennel as its nursery plant, was the third most common in 2010; this year, it came in fifth, after the Common Buckeye. The top ten butterfly species accounted for 83% of the insects spotted (82% last year, 85% in 2010).

For those interested in all the species listed in the last three years, and the count by year for each of them: Here it is.